The present invention relates to the characterization of transient behavior of digital signals.
Characterizing the transient behavior of digital signals, i.e. the transition from logical zero to logical one, and vice versa, has become increasing important for designing as well as manufacturing such digital circuits, and is disclosed e.g. in the European Patent application No. 01106632.1, the teaching thereof shall be incorporated herein be reference. For testing a device under test (DUT), usually one or multiple stimulus signals are applied to the DUT and one or multiple response signals onto the stimulus signals are detected and analyzed (e.g. by comparing the detected response signal with an expected response signal).
A standard characterization of digital circuits requires determining the so-called Bit Error Rate (BER), i.e. the ratio of erroneous digital signals (Bits) to the total number of regarded digital signals. Bit Error Rate Testers (BERTs), such as the Agilent® 81250 ParBERT Platform with and Agilent® E4875A User Software and Measurement Software both by the applicant Agilent Technologies, are provided to determine a so-called BER eye diagram as a two-dimensional graphical representation generated using a sweep over delay and threshold of an analyzer. The result is an eye pattern with a BER value dependent on the sampling point for a plurality of sampling points.
Each sampling point is determined by a relative (e.g. delay) time with respect to corresponding transition of a clock signal (usually the system clock for generating the stimulus signals or a clock signal derived therefrom or from the response signal) and a threshold value for comparing the response signal with. The maximum number of sampling points is usually dependent on the resolution of the analyzer. In order to decrease measurement time, the number of sampling points is usually kept as low as possible. The BER eye diagram gives information which BER value can be expected depending on the position of the sampling point within the eye. Parameters like jitter, level noise, phase margin, and quality factor (Q-factor) can be calculated from the BER eye diagram.